Viscosity and pressure are two important physical parameters of a gas that often need to be measured. Viscosity is a measure of fluid (or gas) resistance to gradual deformation by shear or tensile stress. It provides information about thermal-physical property and can also be used to probe intermolecular potentials. See, for example, G. P. Matthews et al., “An effective isotropic pair potential energy function for carbon dioxide,” Chemical Physics Letters, vol. 155, issue 6, pgs. 518-520 (March 1989). In industrial setting, viscosity measurement is also of great importance. For example, the viscosity of hydrocarbon gases is an important factor in the petroleum industry. See, for example, T. C. Davenport, “Viscosity in the petroleum industry,” Physics Education 3, 139 (May 1968). It affects the quantity that can be recovered from a reservoir. In the semiconductor industry, the viscosity data of highly reactive gases used in semiconductor processing are needed to calibrate mass-flow controllers and to model processes such as chemical vapor deposition. See, for example, J. Wilhelm, et al., “An improved Greenspan acoustic viscometer,” International Journal of Thermophysics, vol. 21, issue 5, pgs. 983-997 (September 2000); and K. A. Gillis, et al., “Theory of the Greenspan viscometer,” The Journal of the Acoustical Society of America 114, pgs. 166-173 (July 2003).
The most common viscometers are falling ball viscometers, capillary tube viscometers, oscillating-piston viscometers, vibrational viscometers, and rotational viscometers—most of which measure liquid viscosity. The measurement of gas viscosity is more challenging since the density and the viscosity of gases are much lower. Thus modification of these viscometers is needed in order to measure the viscosity of a gas.
One well-known viscometer for measuring gas viscosity is a double Helmholtz acoustic resonator. See, for example, K. A. Gillis et al., “Greenspan acoustic viscometer for gases,” Rev. Sci. Instr. 67, 1850 (June 1996). The performance of this viscometer device, however, depends on the response function of the system (which is determined by the geometry of the system and the gas properties) and the instrumentation setup is rather complex. As a result, this device cannot be used to measure the viscosity of a wide range of gases.
Gas or vacuum pressure measurement is also routinely needed. Various pressure gauges are already available however they need to be calibrated with other gauge and has limited accuracy. Very accurate vacuum pressure gauge based on gas viscosity measurement can be obtained using a spinning rotor gauge. However, this instrument is complex and expensive.
Therefore, an improved and more cost effective gas analysis apparatus that can be used to measure viscosity and pressure in a wide range of gases would be desirable.